Implantable medical devices for treating irregular contractions of the heart with electrical stimuli are well known. Exemplary implantable devices are defibrillators and pacemakers. Various types of electrical leads for defibrillators and pacemakers have been suggested, many of which are placed transvenously. Such leads are introduced into the patient's vasculature at a venous access site and travel through veins to the sites where the leads' electrodes will be implanted or otherwise contact target coronary tissue. Electrodes for transvenously-placed leads can be implanted in the myocardium of the right atrium or ventricle, or alternatively, another location within the coronary venous system.
Various techniques have been used to facilitate fixation of the foregoing types of leads at the desired implantation sites. For leads implanted within a cardiac chamber, fixation techniques should provide fixation stable enough to withstand natural heart motion and retrograde blood flow which tend to push the lead out of the location into which the electrode is implanted. Additionally, it is desirable to permit and facilitate repositioning or removal of the lead and fixation structures after implantation if necessary or desired.
Internal helixes for fixing leads are known in the art. It is also recognized that the larger the helix is in diameter, the more stable fixation it provides. In a typical lead configuration, a fixation helix is extended and retracted from a position located internally within the lead body or catheter. As such, the size of the fixation helix used to secure lead bodies is limited by the diameter of the lead body or catheter. The size and type of electrode that is placed within the lead is also limited by this configuration.
Accordingly, there is a continuing need for improved devices and methods for fixation of cardiac leads in the coronary system. In particular, there is a need in the art for a fixation approach that effectively secures and stabilizes the lead electrodes in the target coronary location while still permitting subsequent removal of the lead.